Olefinic polymer and process for producing the same

ABSTRACT

The olefinic polymer characterised in that the n-decane-soluble content thereof is 10% by weight or less and the content of a ligand having a cyclopentadienyl structure is 5 ppb by weight or less. The process for producing an olefinic polymer is a process of producing an olefinic polymer by (co)polymerizing olefins in a gas phase using a fluidized-bed reactor, the process comprising: a polymerization step of (co)polymerizing the olefins with allowing a saturated aliphatic hydrocarbon to exist in a concentration of 2 to 30 mol % in the fluidized-bed reactor and a ligand removing step involving a step of bringing the resulting (co)polymer into contact with a ligand-remover and a step of heating said (co)polymer which has been brought into contact with the ligand-remover.

FIELD OF THE INVENTION

The present invention relates to an olefinic polymer and a process forproducing the same, and more specifically, to an olefinic polymer havinglow content of components that might generate odors and of componentsthat might change taste and to a process for producing such an olefinicpolymer in an efficient manner.

BACKGROUND OF THE INVENTION

Olefinic polymers such as polyethylenes, polypropylene,ethylene/α-olefin copolymers and propylene/α-olefin copolymers arewidely used for various molding materials and the like. Thecharacteristics required for these olefinic polymers differ depending onthe use thereof. For example, the olefinic polymer for food use isrequired not to damage the taste of foods because a delicate smell andtaste are regarded as important.

In the meantime, when, in the production of an olefinic polymer, olefinsare polymerized by a vapor phase polymerization method in the presenceof a solid state catalyst, the polymer can be obtained in the form of aparticle and such as a step of precipitating a polymer and a step ofseparating solvents after polymerization become needless. Therefore,this is known to be able to simplify the production process and toreduce the production cost. However, the olefinic polymer produced by avapor phase polymerization method sometimes exudes an odor whenprocessed with heat and this may affect flavors and the like especiallywhen the olefinic polymer is employed for food use where a delicatesmell and taste are regarded as important. Therefore, the use of thesepolymers are occasionally limited in such uses.

As a method of reducing the influence of the odor of the olefinicpolymer obtained by a vapor phase polymerization method and theinfluence of the olefinic polymer on taste when it is used for fooduses, for example, a method is described in the publication of JapanesePatent Application Laid-Open No. 10-45824 for decreasing the odoremanated from the olefinic polymer during molding by contacting theolefinic polymer obtained using a metallocene catalyst with steam andthe like to decompose the cyclopentadienyl ligand in the polymer.

Although the odor of the olefinic polymer can be considerably decreasedby the method like this, it has been desired to further decrease odorsin food use and the like in recent years.

In this situation, the inventors of the present invention have madestudies and, consequently reached to the completion of the presentinvention with a finding that upon producing a olefinic polymer by avapor phase polymerization method, the odor is greatly reduced bycarrying out the polymerization reaction in the presence of a saturatedaliphatic hydrocarbon in a fluidized bed reactor and then contacting theobtained polymer with steam and the like.

OBJECT OF THE INVENTION

Accordingly, it is an object of the invention to provide an olefinicpolymer having the reduced content of components that might emanateodors and of components that might change tastes and also to provide aprocess for producing the olefinic polymer.

SUMMARY OF THE INVENTION

An olefinic (co)polymer according to the present invention is a olefinic(co)polymer obtained by polymerizing at least one selected from ethyleneand α-olefins having 3 to 20 carbon atoms in the presence of ametallocene type catalyst, wherein the n-decane-soluble content is 10%by weight or less and the content of a ligand having a cyclopentadienylstructure is 5 ppb by weight or less.

The olefinic polymer is preferably a copolymer of ethylene and at leastone α-olefin selected from α-olefins having 3 to 20 carbon atoms.

Also, the olefinic polymer preferably has a density of 0.930 g/cm³ orless.

Further, the olefinic polymer is preferably the one obtained by(co)polymerizing one or two or more olefins selected from ethylene andα-olefins having 3 to 20 carbon atoms in a vapor phase usingfluidized-bed reactor.

Furthermore, the olefinic polymer is preferably the one obtained by(co)polymerizing one or two or more olefins selected from ethylene andα-olefins having 3 to 20 carbon atoms with allowing a saturatedaliphatic hydrocarbon having 2 to 10 carbon atoms to exist with aconcentration of 2 to 30 mol % in a fluidized bed reactor, then bringingthe resulting (co)polymer into contact with a ligand-remover and thenheating the (co)polymer which has been brought into contact with theligand-remover.

A process for producing an olefinic polymer according to the presentinvention is a process of producing an olefinic polymer by(co)polymerizing one or two or more olefins selected from ethylene andα-olefins having 3 to 20 carbon atoms in the presence of a metallocenetype catalyst in a gas phase using a fluidized-bed reactor, the processcomprising:

a polymerization step of (co)polymerizing olefins with allowing asaturated aliphatic hydrocarbon to exist with a concentration of 2 to 30mol % in the fluidized-bed reactor; and

a ligand removing step involving a step of bringing the resulting(co)polymer into contact with a ligand-remover and a step of heating the(co)polymer which has been brought into contact with the ligand-remover.

In the present invention, the above saturated aliphatic hydrocarbon ispreferably supplied to a fluidized-bed reactor in the vapor-liquidtwo-phase coexisting state.

The process for producing an olefinic polymer can produce an olefinicpolymer having the n-decane-soluble content of 10% by weight or less andthe content of 5 ppb by weight or less for a ligand having acyclopentadienyl structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory view showing the case of carrying out apolymerization step in single stage.

FIG. 2 is an explanatory view showing the case of carrying out apolymerization step in two stages.

FIG. 3 is an explanatory view representing one example of a ligandremoving step.

FIG. 4 is an explanatory view representing another example of a ligandremoving step.

DETAILED DESCRIPTION OF THE INVENTION

An olefinic polymer according to the present invention and a process forproducing the olefinic polymer will be hereinafter explained in detail.

It should be noted that there is the case where the term“polymerization” is used in terms of meanings implying not onlyhomopolymerization but also copolymerization, and also there is the casewhere the term “polymer” is used in terms of not only a homopolymer butalso a copolymer.

[Olefinic Polymer]

The olefinic polymer according to the present invention is a (co)polymerof one or two or more olefins selected from ethylene and α-olefinshaving 3 to 20 carbon atoms.

Here, specific examples of the α-olefins having 3 to 20 carbon atomsinclude propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene,1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene,1-octadecene and 1-eicosene. Among these compounds, α-olefins having 3to 10 and particularly 5 to 8 carbon atoms are preferably used.

The olefin selected from ethylene and these α-olefins having 3 to 20carbon atoms may be used alone or in combination of two or more of them.

In the present invention, the olefinic polymer is preferably a copolymerof ethylene and at least one α-olefin selected from α-olefins having 3to 20 carbon atoms and more preferably a copolymer of ethylene and atleast one α-olefin selected from α-olefins having 3 to 10 carbon atoms.

When the olefinic polymer according to the present invention is acopolymer of ethylene and at least two or more monomers selected fromα-olefins having 3 to 20 carbon atoms, no particular limitation isimposed on the proportion of the content of each structural unit.However, for example, when the copolymer is a copolymer of ethylene andan α-olefin, the copolymer preferably contains 80 to 99.6 mol % and morepreferably 93.8 to 98 mol % of a structural unit derived from ethylene,and preferably 0.4 to 20 mol % and more preferably 2 to 6.2 mol % of astructural unit derived from the α-olefin.

Also, in the present invention, the olefinic polymer may contain astructural unit derived from polyenes depending on the need togetherwith the structural units derived from ethylene and α-olefins having 3to 20 carbon atoms. For example, the olefinic polymer may containstructural units derived from conjugate dienes such as butadiene andisoprene and from non-conjugate dienes such as 1,4-hexadiene,dicyclopentadiene and 5-vinyl-2-norbornene.

The n-decane-soluble content of the olefinic polymer according to thepresent invention is 10% by weight or less, preferably 5% by weight orless and more preferably 3% by weight or less. The lower limit of then-decane-soluble content is preferably 0% by weight, but substantially0.1% by weight which is a measurable limit.

Since the olefinic polymer whose a n-decane-soluble content falls withinthe above range has the reduced content of low-molecular weightcomponents such as oligomers, less odor emanates from the olefinicpolymer during molding and also, the olefinic polymer scarcely damages adelicate smell and taste when it is employed in food uses.

The n-decane-soluble content is measured in the following manner.Specifically, an one-liter flask equipped with a stirring device ischarged with 3 g of a polymer sample, 20 mg of2,6-di-tert-butyl-4-methylphenol and 500 ml of n-decane and the mixtureis dissolved at 145° C. in an oil bath by heating. After the polymersample is dissolved, the mixture is cooled to ambient temperature overabout 8 hours and in succession, kept in a 23° C. water bath for 8hours. The precipitated polymer (n-decane-insoluble part) is separatedfrom a n-decane solution containing a dissolved polymer by filtrationusing a G-4 (or G-2) glass filter. The solution obtained in this manneris heated under the condition of 10 mmHg and 150° C. to dry the polymerdissolved in the n-decane solution till the weight of the polymerbecomes constant and the weight is defined as the n-decane-solublecontent.

Also, in the olefinic polymer according to the present invention, thecontent of a ligand having a cyclopentadienyl structure is 5 ppb byweight or less, preferably 2 ppb by weight or less and more preferably 1ppb by weight or less. The lower limit of the content of the ligandhaving a cyclopentadienyl structure is preferably 0 ppb by weight, butsubstantially 1 ppb by weight which is a measurable limit.

When the content of the ligand having a cyclopentadienyl structure iswithin the above range, less odors emanates from the olefinic polymerduring molding and also, the olefinic polymer scarcely damages adelicate smell and taste when it is employed in food uses.

The content of the ligand having a cyclopentadienyl structure ismeasured in the following manner. Specifically, the ligand having acyclopentadienyl structure is extracted using toluene and identified andmeasured quantitatively by gas chromatograph mass spectrometer using acalibration curve method.

The olefinic polymer according to the present invention has thecharacteristics that the number average molecular weight (Mn) measuredby gel permeation chromatography (GPC) falls in a range from, typically,1,250 to 8,500, the Mw/Mn falls in a range from typically 1.8 to 3.5 andpreferably 1.9 to 2.3, the density measured by a density gradient methodis typically 0.930 g/cm³ or less and preferably in a range from 0.880 to0.930 g/cm³.

The olefinic polymer according to the present invention asaforementioned is obtained by (co)polymerizing one or two or moreolefins selected from ethylene and α-olefins having 3 to 20 carbon atomsin a vapor phase using, for example, a fluidized-bed reactor.

To state more concretely, the olefinic polymer is obtained by(co)polymerizing one or two or more olefins selected from ethylene andα-olefins having 3 to 20 carbon atoms with allowing a saturatedaliphatic hydrocarbon to exist in a fluidized-bed reactor, then bringingthe obtained (co)polymer into contact with a ligand remover and thenheating the (co)polymer which is made to be in contact with theligand-remover.

[Process for Producing the Olefinic Polymer]

The process for producing the olefinic polymer according to the presentinvention comprises:

a polymerization step of (co)polymerizing olefins in the presence of asaturated aliphatic hydrocarbon in a fluidized-bed reactor; and

a ligand removing step of bringing the obtained (co)polymer into contactwith the ligand-remover and then heating the (co)polymer which has beenmade to be in contact with the ligand-remover. The process will now bedescribed by way of embodiment in conjunction with the accompanyingdrawings.

(Polymerization Step)

In the polymerization step, at the fluidized-bed where a solid particlecontaining a catalyst is maintained in a fluidized state by means of agas stream flowing containing a polymerizable monomer through the insideof the fluidized bed reactor, the polymerization reaction is carried outby introducing a saturated aliphatic hydrocarbon in a gas-liquid mixedstate together with the polymerizable monomer from the bottom of thefluidized-bed reactor upon producing an olefinic polymer by polymerizingat least one olefin selected from ethylene and α-olefins having 3 to 20carbon atoms (polymerizable monomer) in a vapor phase under the presenceof the catalyst.

Here, the polymerization step will be explained in detail with referenceto FIG. 1. Incidentally, the FIG. 1 shows only the polymerization stepand the ligand removing step is omitted.

In the polymerization step, the catalyst is supplied from a line 15 in afluidized-bed reactor 11, and also the polymerizable monomers andsaturated aliphatic hydrocarbon supplied from a supply line 12 arepassed through the reactor by blowing the mixture into the fluidized bed18 from a supply port 9 through a diffusing plate 17 such as aperforated plate disposed on the under part of the reactor and bydischarging the gas stream from a line 16 disposed on the upper portionof the reactor to keep the solid particles (the solid catalyst andproduced polymer) in a fluidizing state by this gas stream (fluidizinggas), whereby the fluidized bed (reaction system) 18 is formed.

The polymer particle produced by the polymerization of at least oneolefin selected from ethylene and olefins having 3 to 20 carbon atoms inthe fluidized bed 18 in this manner is withdrawn continuously orintermittently from the reactor through a discharge line 10 and thensupplied to the ligand decomposing step as will be described later.

On the other hand, the gas discharged from the reactor 11 through theline 16 contains the unreacted polymerizable monomer and saturatedaliphatic hydrocarbon and the like and is typically circulated as acirculating gas to the reactor 11 through the supply port 9 aftercooling.

The fluidizing gas consisting of the polymerizable monomer and thecirculating gas is introduced from the supply port 9 to the reactor 11as aforementioned and passed through the fluidized-bed 18 at such a flowrate that the fluidized bed 18 can be kept in a fluidizing state by thegas. Specifically, the flow rate of the gas introduced from the supplyport 9 is about 3 U_(mf) to 50 U_(mf) and preferably about 5 U_(mf) to30 U_(mf), where U_(mf) is the minimum fluidizing rate of the fluidizedbed. It is possible to stir the fluidized bed 18 mechanically, forexample, using various stirrers such as an anchor type stirrer, screwtype stirrer and ribbon type stirrer.

The polymerization step may be divided into two or more stages differingin reaction condition from each other to carry out the polymerization.Next, the polymerization step in the case of carrying out thepolymerization in two or more stages will be explained in detail withreference to FIG. 2, where the ligand removing step is also omitted inthe FIG. 2.

In the case of carrying out the polymerization in two or more stages,for example, in the case of carrying out the polymerization is carriedout in a multistage vapor phase polymerization apparatus having twovapor phase fluidized-bed reactors which are serially connected, thepolymerization is conducted as follows.

In the multi stage vapor phase polymerization apparatus, a firstfluidized-bed reactor 11 is connected serially to a second fluidized-bedreactor 21 as shown in, for example, FIG. 2.

Specifically, it is so designed that the catalyst is supplied from asupply line 15 and also, gas (fluidizing gas) containing a gaseousolefin (polymerizable monomers) and the saturated aliphatic hydrocarbonis supplied from the bottom of the first fluidized-bed reactor 11 from asupply line 12 through a blower 13. The supplied fluidized-bed gas isblown into a fluidized-bed 8 through a diffusing plate 7 made of aperforated plate or the like disposed in the vicinity of the bottom ofthe first fluidized-bed reactor 11 and discharged from the upper part ofthe fluidized-bed reactor 11, and thus the fluidizing gas passes throughthe inside of the fluidized-bed reactor. The solid particles (the solidcatalyst and the produced polymer) is kept in a fluidizing state by thegas flow of the gas passing through the inside of the fluidized-bedreactor 11, whereby the fluidized bed 18 is formed.

Then, the produced polymer particle is withdrawn continuously orintermittently and subjected to solid-vapor separation using solid-vaporseparators 31 and 32. At this time, valves 33 and 34 are properly openedand shut under control. The polymer particle withdrawn in this manner isdischarged in a transport line 25 by the action of the valve 35 and fedto the second fluidized-bed reactor 21 through the transport line 25.

Also, the unreacted gaseous olefin, saturated aliphatic hydrocarbon andthe like which have passed through the fluidized bed 18 are deceleratedin its flow rate in a decelerating region 19 disposed on the upper partof the first fluidized-bed reactor 11 and discharged out of the firstfluidized-bed reactor 11 through a gas discharge port disposed on theupper part of the first fluidized-bed reactor 11.

The unreacted gaseous olefin, saturated aliphatic hydrocarbon and thelike discharged from the first fluidized-bed reactor 11 are cooled in aheat exchanger (cooling unit) 14 through a circulating line 16,connected in the supply line 12 and supplied continuously again to theinside of the fluidized bed 18 in the first fluidized-bed reactor 11 bya blower 13. In the heat exchanger 14, the circulating gas is typicallycooled to a temperature close to the dew point of the gas. The dew pointof the gas means the temperature at which a liquid condensate starts.When the circulating gas is cooled to a temperature lower than the dewpoint and supplied to the fluidized bed 18, reaction heat can be removedby the latent heat of vaporization of the liquid condensate to therebyimprove heat-removal efficiency in the fluidized bed 18. It should benoted that when circulating the circulating gas in the fluidized-bedreactor 11, a part of the circulating gas may be purged from an optionalplace of the circulating line 16.

On the other hand, the polymer particles withdrawn from a discharge line30 of the first fluidized-bed reactor 11 through the solid-vaporseparators 31 and 32 are fed to the second fluidized-bed reactor 21through the transport line 25. The transport line 25 is branched fromthe supply line 22 and the other end of the transport line 25 isconnected to the upper side of the second fluidized-bed reactor 21.Through the transport line 25, the pressure of the gas containing theolefins and the saturated aliphatic hydrocarbon fed from the supply line22 is raised by a pressure-rise means such as a centrifugal blower 41,also the polymer particles withdrawn from the first fluidized-bedreactor 11 is made to be entrained in this gas to transport the polymerparticles and then introduced into the second fluidized-bed reactor 21.Also, a new gaseous olefin (polymerizable monomer) and saturatedaliphatic hydrocarbon are supplied to the second fluidized-bed reactor21 from the supply line 22 through a blower 23 by the transport line 25and at the same time, they also supplied as a fluidizing gas to thebottom of the second fluidized-bed reactor 21. It should be noted thatalthough a new catalyst is not supplied to the second fluidized-bedreactor 21 in general, a new solid catalyst may be supplied to a desiredplace of the fluidized-bed reactor through, for example, the transportline 25 according to the need.

The fluidizing gas supplied from the bottom of the second fluidized-bedreactor 21 is blown into a fluidized bed 28 through a diffusing plate 27made of a perforated plate or the like disposed in the vicinity of thebottom of the second fluidized-bed reactor 21 and discharged from theupper part of the fluidized-bed reactor 21, and thus passed through thefluidized-bed reactor 21. The gas stream of the gas passing through thefluidized-bed reactor 21 keeps the solid particles (the aforementionedpolymer particles and the produced polymer) in a fluidizing state tothereby form the fluidized bed 28. At this time, a copolymerizationreaction is run in the fluidized bed 28.

Then, the polymer particle obtained in the second fluidized-bed reactor21 is withdrawn continuously or intermittently from a discharge line 40and supplied to the ligand removing step as will be described later.

Also, the unreacted gaseous olefin, saturated aliphatic hydrocarbon andthe like which have passed through the fluidized bed 28 are deceleratedin its flow rate in a decelerating region 29 disposed on the upper partof the second fluidized-bed reactor 21 and discharged out of the secondfluidized-bed reactor 21 through a gas discharge port disposed on theupper part of the second fluidized-bed reactor 21.

The unreacted gaseous olefins, saturated aliphatic hydrocarbon and thelike discharged from the second fluidized-bed reactor 21 are cooled in aheat exchanger (cooling unit) 24 through a circulating line 26,connected in the supply line 22 and supplied continuously again to theinside of the fluidized bed 28 in the second fluidized-bed reactor 21 bya blower 23. In the heat exchanger 24, the circulating gas is typicallycooled to a temperature close to the dew point of the gas. When thecirculating gas is cooled to a temperature lower than the dew point andsupplied to the fluidized bed 28, reaction heat can be removed by thelatent heat of vaporization of the liquid condensate to thereby improveheat-removal efficiency in the fluidized bed 28. It should be noted thatwhen circulating the circulating gas to the fluidized-bed reactor 21, apart of the circulating gas may be purged from an optional place of thecirculating line 26.

In the first fluidized-bed reactor 11, as aforementioned, the fluidizinggas is passed through the fluidized-bed 18 at such a flow rate that thefluidized bed 18 can be kept in a fluidizing state. In the secondfluidized-bed reactor 21, the fluidizing gas is passed through thefluidized-bed 28 at such a flow rate that the fluidized bed 28 can bekept in a fluidizing state.

Specifically, the flow rate of the gas introduced from the bottom ofeach reactor through the supply lines 12 and 22 is about 3 U_(mf) to 50U_(mf) and preferably about 5 U_(mf) to 30 U_(mf) , where U_(mf) is theminimum fluidizing rate of the fluidized bed. It is possible to stir thefluidized bed 18 mechanically, for example, using various stirrers suchas an anchor type stirrer, screw type stirrer and ribbon type stirrer.

Although the above explanations were furnished as to a multistage vaporphase polymerization apparatus consisting of two fluidized-bed reactors,namely the first fluidized-bed reactor 11 and the second fluidized-bedreactor 21 which are serially connected to each other, even a multistagevapor phase apparatus consisting of three or more fluidized-bed reactorscan be structured in the same manner.

In the fluidized bed kept in a fluidizing state as aforementioned in thepresent invention, the polymerization monomers supplied to the reactor,specifically, at least one olefin selected from ethylene and α-olefinshaving 3 to 20 carbon atoms is polymerized.

In the present invention, polyenes and the like may be optionallycopolymerized together with the above olefins. For example, conjugatedienes such as butadiene and isoprene or non-conjugate dienes such as1,4-hexadiene, dicyclopentadiene and 5-vinyl-2-norbornene may becopolymerized.

In the polymerization step, no particular limitation is imposed on theamount of each monomer to be supplied in the case of copolymerizing twoor more monomers selected from ethylene and α-olefins having 3 to 20carbon atoms. However, in the case of copolymerizing, for example,ethylene with an α-olefin having 3 to 20 carbon atoms, the α-olefin issupplied in an amount of typically 0.015 to 0.15 mole and preferably0.02 to 0.08 mole based on one mole of ethylene.

In the present invention, the saturated aliphatic hydrocarbon in avapor-liquid mixed state is introduced together with the polymerizablemonomer from the bottom of the reactor to conduct the above reaction.Specific examples of such a saturated aliphatic hydrocarbon includesaturated aliphatic hydrocarbons having 2 to 10 carbon atoms such asethane, propane, n-butane, i-butane, n-pentane, i-pentane, hexane,heptane, octane, nonane, decane, 2,2-dimethylpropane,2,2-dimethylbutane, 2,3-dimethylbutane, 2,2,3-trimethylbutane,2-methylpentane, 3-methylpentane, 2,2-dimethylpentane,3,3-dimethylpentane, 2,3-dimethylpentane, 2,4-dimethylpentane,2-methylhexane, 3-methylhexane, 4-methylhexane, 2,3-dimethylhexane,cyclopentane, cyclohexane, methylcyclopentane and dimethylcyclopentane.Among these, those having 3 to 8 carbon atoms are preferable.

In the present invention, a process may be adopted in which using two ormore saturated aliphatic hydrocarbons, at least one saturated aliphatichydrocarbon is introduced in a vapor-liquid mixed state into apolymerizing vessel and the other saturated aliphatic hydrocarbon isintroduced in a gaseous state into the polymerizing vessel. In thiscase, as the saturated aliphatic hydrocarbon to be introduced in agaseous state into the reactor, ethane, propane, n-butane, i-butane,i-pentane, n-pentane, hexane or the like is preferable and these may beused in combination.

Here, the gaseous saturated aliphatic hydrocarbon means thatsubstantially all the saturated aliphatic hydrocarbon exists as a gasphase, specifically 99% or more of 100% of the total saturated aliphatichydrocarbon exists as a gaseous phase, namely, means that the vaporfraction is 0.99 or more. The ratio of the existence of the gas phasecan be obtained from the vapor-liquid equilibrium constant K_(i) basedon the method of Soave-Redlich-Kwong reported in Chem. Eng. Sci.,27,1197 (1972).

As the saturated aliphatic hydrocarbon to be introduced in avapor-liquid mixed state into the reactor, those which have a higherboiling point than the saturated aliphatic hydrocarbon to be introducedin a gaseous state into the reactor and are easily condensed when cooledin a heat exchanger or the like are selected. As the saturated aliphatichydrocarbon, for example, i-pentane, n-pentane, hexane or heptane ispreferable and these hydrocarbons may be used in combination.

In the present invention, when using the saturated aliphatic hydrocarbonto be introduced in a vapor-liquid mixed state in combination with thesaturated aliphatic hydrocarbon to be introduced in a gaseous state,especially, a combination of ethane and i-pentane or a combination ofethane and hexane is preferably used.

In the composition (that is, substantially the composition of the gas ofthe fluidized-bed reaction system) discharged from the reactor, theconcentration of the saturated aliphatic hydrocarbon in the gas istypically about 2 to 30 mol % and preferably about 5 to 20 mol % thoughit differs depending on the number of carbon atoms in the saturatedaliphatic hydrocarbon, polymerization temperature, the flow rate of thefluidizing gas and the like.

Also, when using the saturated aliphatic hydrocarbon to be introduced ina vapor-liquid mixed state in combination with the saturated aliphatichydrocarbon to be introduced in a gaseous state, it is preferable thatthe concentration (saturated aliphatic hydrocarbon to be introduced in agaseous state)/(saturated aliphatic hydrocarbon to be introduced in avapor-liquid mixed state) in the discharged gas be 60 to 100% by weight.

Although the saturated aliphatic hydrocarbon is introduced together withthe polymerizable monomer into the reactor from the supply line throughthe supply port of the bottom of the reactor in usual as aforementioned,these hydrocarbons maybe introduced from the same place or separatelyfrom different places.

The polymerization of ethylene and at least one α-olefin selected fromα-olefins having 3 to 20 carbon atoms which polymerization is carriedout in the presence of the saturated aliphatic hydrocarbon on thefluidized-bed is desirably carried out under the condition of apolymerization pressure of typically 0.1 to 10 MPa and preferably 0.2 to4 MPa at a polymerization temperature of typically 20 to 130° C.,preferably 50 to 120° C. and more preferably 70 to 110° C. though theseconditions differ depending on the type and proportion of olefin to bepolymerized, the proportion of the saturated aliphatic hydrocarbon andthe fluid condition of the fluidized bed.

The above copolymerization may be carried out in the presence of amolecular weight regulator such as hydrogen molecule according to theneed and the regulator may be supplied from a desired place.

The saturated aliphatic hydrocarbon as aforementioned is anon-polymerizable hydrocarbon. When it is once supplied to the reactor,it is not consumed by the polymerization reaction, but is typicallywithdrawn from the discharge line together with the unreactedpolymerizable monomers and circulated as the fluidizing gas to thereactor.

Specifically, this discharged gas may contain the saturated aliphatichydrocarbons in a total amount of 0.8 to 80 mol %, however, this amountdiffers depending on the number of carbon atoms in the saturatedaliphatic hydrocarbon.

The gas discharged from the reactor is typically introduced into a heatexchanger and cooled therein to remove polymerization heat and thencirculated as the circulating gas to the reactor from the supply port.The saturated aliphatic hydrocarbon cooled in the heat exchanger at thistime is circulated in a vapor-liquid mixed state to the reaction system.When the discharge gas is circulated to the reactor in this manner, apart of the discharge gas may be purged.

In the present invention, the molecular weight of the resulting olefinicpolymer may be adjusted by changing the polymerization condition such aspolymerization temperature or may be adjusted by controlling the amountof hydrogen molecule (molecular weight regulator) to be used.

As aforementioned, the gaseous saturated aliphatic hydrocarbon and thesaturated aliphatic hydrocarbon in a vapor-liquid mixed state areintroduced into the reactor to polymerize ethylene and at least oneα-olefin selected from α-olefins having 3 to 20 carbon atoms, so thatlow-molecular weight components in the produced polymers are removed bythese saturated aliphatic hydrocarbons, whereby a polymer having thegreatly reduced content of n-decane-soluble components can be obtained.Also, the polymerization heat of the fluidized bed can be removed by thelatent heat of the saturated aliphatic hydrocarbon introduced in avapor-liquid mixed state.

In the present invention, the olefinic polymer fulfilling the propertiesas mentioned above is obtained in the case of using a metallocene typecatalyst though the polymerization as aforementioned may be carried outusing a wide range of catalysts known as catalysts for ethylenepolymerization such as Ziegler type catalysts, Philip type chromiumoxide catalysts and metallocene type catalysts. Specific examples of themetallocene type catalysts preferably used in the present inventioninclude:

(A) metallocene compounds of transition metals selected from the IVBgroup in the periodic table; and

(B) (B-1) organic aluminum oxy compounds;

-   -   (B-2) organic aluminum compounds; and    -   (B-3) at least one compound selected from compounds which react        with the metallocene compound (A) to form an ion pair.

((A) Metallocene Compound)

The metallocene compound (A) of transition metals selected from the IVBgroup in the periodic table are specifically represented by thefollowing formula (i).ML_(x)  (i)wherein M represents a transition metal selected from Zr, Ti, Hf, V, Nb,Ta and Cr, L represents a ligand coordinating with the transition metalwherein at least one L is a ligand having a cyclopentadienyl structureand L other than the ligand having a cyclopentadienyl structure is ahydrogen atom, a halogen atom, a hydrocarbon group having 1 to 12 carbonatoms, an alkoxy group, an aryloxy group, a trialkylsilyl group or aSO₃R group (where R is a C₁–C₈ hydrocarbon group which may have asubstituent such as a halogen) and x represents the atomic value of thetransition metal.

As the ligand having a cyclopentadienyl structure, alkyl substitutedcyclopentadienyl groups such as a cyclopentadienyl group,methylcyclopentadienyl group, dimethylcyclopentadienyl group,trimethylcyclopentadienyl group, tetramethylcyclopentadienyl group,pentamethylcyclopentadienyl group, ethylcyclopentadienyl group,methylethylcyclopentadienyl group, propylcyclopentadienyl group,methylpropylcyclopentadienyl group, butylcyclopentadienyl group,methylbutylcyclopentadienyl group and hexylcyclopentadienyl group, anindenyl group and 4,5,6,7-tetrahydroindenyl group and a fluorenyl groupmay be exemplified. These groups may be substituted with a halogen atom,trialkylsilyl group or the like.

Among these groups, alkyl substituted cyclopentadienyl group isparticularly preferable.

Specific examples of the ligand other than the ligand having acyclopentadienyl structure are as follows. Examples of the halogeninclude fluorine, chlorine, bromine and iodine. Examples of thehydrocarbon group having 1 to 12 carbon atoms include alkyl groups suchas methyl group, ethyl group, propyl group, isopropyl group and butylgroup, cycloalkyl groups such as cyclopentyl group and cyclohexyl group,aryl groups such as phenyl group and tolyl group and aralkyl groups suchas benzyl group and neophyl group. Examples of the alkoxy group includemethoxy group, ethoxy group and butoxy group. Examples of the aryloxygroup include phenoxy group. Examples of the SO₃R group includep-toluene sulfonate group, methane sulfonate group and trifluoromethanesulfonate group.

When the compound represented by the above general formula has two ormore groups having a cyclopentadienyl structure, two groups of thosegroups having a cyclopentadienyl structure may be bonded with each otherthrough an alkylene group such as ethylene or propylene, a substitutedalkylene group such as isopropylidene or diphenylmethylene, a silylenegroup or substituted silylene group such as dimethylsilylene group,diphenylsilylene group or methylphenylsilylene group.

The metallocene compounds containing such a ligand having acyclopentadienyl structure are represented more specifically by thefollowing formula (ii) when the valence of the transition metal is, forexample, 4.R² _(k)R³ ₁R⁴ _(m)R⁵ _(n)M  (ii)wherein M represents the foregoing transition metal, R² represents agroup (ligand) having a cyclopentadienyl structure, R³, R⁴ and R⁵represent groups having a cyclopentadienyl structure or other groups asaforementioned, k denotes an integer of 1 or more and k+1+m+n=4.

In the present invention, metallocene compounds represented by R² _(k)R³₁R⁴ _(m)R⁵ _(n)M in which at least two, for example, R² and R³, amongR², R³, R⁴ and R⁵ are groups (ligands) having a cyclopentadienylstructure are preferably used. These groups having a cyclopentadienylstructure maybe bonded with each other through an alkylene group,substituted alkylene group, silylene group or substituted silylenegroup.

Examples of the metallocene compounds as aforementioned, when,specifically, M is zirconium, include bis(cyclopentadienyl)zirconiumdichloride, bis(cyclopentadienyl)zirconium dibromide,bis(cyclopentadienyl)dimethylzirconium,bis(cyclopentadienyl)diphenylzirconium,bis(cyclopentadienyl)dibenzylzirconium, bis(cyclopentadienyl)zirconiumbis(methanesulfonate), bis(cyclopentadienyl)zirconiumbis(p-toluenesulfonate), bis(cyclopentadienyl)zirconiumbis(trifluoromethanesulfonate), bis(methylcyclopentadienyl)zirconiumdichloride, bis(dimethylcyclopentadienyl)zirconium dichloride,bis(ethylcyclopentadienyl)zirconium dichloride,bis(methylethylcyclopentadienyl)zirconium dichloride,bis(propylcyclopentadienyl)zirconium dichloride,bis(methylpropylcyclopentadienyl)zirconium dichloride,bis(butylcyclopentadienyl)zirconium dichloride,bis(methylbutylcyclopentadienyl)zirconium dichloride,bis(trimethylcyclopentadienyl)zirconium dichloride,bis(indenyl)zirconium dichloride, bis(indenyl)zirconium dibromide,bis(4,5,6,7-tetrahydroindenyl)zirconium dichloride,bis(fluorenyl)zirconium dichloride, ethylenebis(indenyl)zirconiumdichloride, ethylenebis(indenyl)zirconium dibromide,ethylenebis(indenyl)dimethylzirconium,isopropylidene(cyclopentadienyl-fluorenyl)zirconium dichloride,isopropylidene(cyclopentadienyl-methylcyclopentadienyl)zirc oniumdichloride, dimethyl silylenebis(cyclopentadienyl)zirconium dichloride,dimethylsilylenebis(methylcyclopentadienyl)zirconium dichloride,dimethylsilylenebis(dimethylcyclopentadienyl)zirconium dichloride,dimethylsilylenebis (indenyl) zirconium dichloride,dimethylsilylenebis(2-methylindenyl)zirconium dichloride,dimethylsilylenebis(2-methyl-4-isopropylindenyl)zirconium dichloride,dimethylsilylene(cyclopentadienyl-fluorenyl)zirconium dichloride,diphenylsilylenebis (indenyl) zirconium dichloride andmethylphenylsilylenebis(indenyl)zirconium dichloride.

It should be noted that in the above examples, the di-substituted formof a cyclopentadienyl ring includes 1,2- and 1,3-disubstituted forms andthe tri-substitution form of a cyclopentadienyl ring includes 1,2,3- and1,2,4-trisubstitution forms. Also, the alkyl groups such as propyl andbutyl include isomers such as n-, i-, sec- and tert-isomers.

Compounds obtained by substituting zirconium with titanium, hafnium,vanadium, niobium, tantalum or chromium in the metal locene compounds asmentioned above may be exemplified.

In the present invention, as the metallocene compound (A), zirconiummetallocene compounds having a ligand containing at least twocyclopentadienyl structures are preferably used.

These metallocene compounds (A) may be used alone or in combination oftwo or more.

((B-1) Organic Aluminum Oxy Compound)

The (B-1) organic aluminum oxy compound may be a conventionally knownbenzene-soluble aluminoxane and also a benzene-insoluble organicaluminum oxy compound as disclosed in the publication of Japanese PatentApplication Laid-Open No. 2-276807.

This aluminoxane may contain a small amount of organic metal components.Also, an aluminoxane obtained by decomposing solvents or unreactedorganic aluminum compounds from a recovered aluminoxane solution bydistillation maybe used by re-dissolving it in a solvent.

Given as specific examples of the organic aluminum compound used in theproduction of aluminoxane are those described later as the organicaluminum compound (B-2). These compounds may be used in combination oftwo or more of them.

Among these compounds, a trialkylaluminum and tricycloalkylaluminum areparticularly preferable.

Also, the benzene-insoluble organic aluminum oxy compound contains analuminum component soluble in benzene at 60° C. in an amount of 10% orless, preferably 5% or less and particularly preferably 2% or less as anAl atom and is insoluble or hardly soluble in benzene.

The solubility of such an organic aluminum oxy compound in benzene isdetermined in the following manner. Specifically, the organic aluminumoxy compound of 100 mmol of Al is suspended in 100 ml of benzene andthen mixed at 60° C. for 6 hours with stirring. The suspension issubjected to filtration using a jacketed G-5 glass filter at 60° C.under heating and the solid part separated on the filter is washed with50 ml of benzene at 60° C. four times. Then, the existing amount (×mmol) of Al atoms present in the entire filtrates is measured (× %).

The organic aluminum oxy compound (B-1) may be used alone or incombination of two or more.

((B-2) Organic Aluminum Compound)

The organic aluminum compound (B-2) is represented by, for example, thefollowing formula (iii).R¹ _(n)nAlX_(3−n)  (iii)wherein the formula (iii) , R¹ represents a hydrocarbon group having 1to 12 carbon atoms, X represents a halogen atom or hydrogen atom and ndenotes a number from 1 to 3.

In the above formula (iii), R¹ represents a hydrocarbon group having 1to 12 carbon atoms, for example, an alkyl group, cycloalkyl group oraryl group and specifically methyl group, ethyl group, n-propyl group,isopropyl group, isobutyl group, pentyl group, hexyl group, octyl group,cyclopentyl group, cyclohexyl group, phenyl group and tolyl group.

Specific examples of the organic aluminum compound (B-2) like this mayinclude trialkylaluminums such as trimethylaluminum, triethylaluminum,triisopropylaluminum and triisobutylaluminum; alkenylaluminums such asisoprnylaluminum; dialkylaluminum halides such as dimethylaluminumchloride, diethylaluminum chloride, diisopropylaluminum chloride anddiisobutylaluminum chloride; alkylaluminum sesquihalides such asmethylaluminum sesquichloride, ethylaluminum sesquichloride andisopropylaluminumsesquichloride; alkylaluminum dihalides such asmethylaluminum dichloride, ethylaluminum dichloride andisopropylaluminum dichloride; and alkylaluminum hydrides such asdiethylaluminum hydride and diisobutylaluminum hydride.

Also, as the organic aluminum compound (B-2), compounds as shown by thefollowing formula (iv) may be used.R¹ _(n)AlY_(3−n)  (iv)wherein the formula (iv) R¹ is the same as above, Y represents an —OR²group, an —OSiR³ ₃ group, an —OALR⁴ ₂ group, a —NR⁵ ₂ group, a —SiR⁶ ₃group or a —N(R⁷)AlR⁸ ₂ group, n denotes a number of 1 to 2, R², R³, R⁴and R⁸ respectively represent methyl group, ethyl group, isopropylgroup, isobutyl group, cyclohexyl group or phenyl group, R⁵ represents ahydrogen atom, methyl group, ethyl group, isopropyl group, phenyl group,trimethylsilyl group or the like and R⁶ and R⁷ respectively representmethyl group or ethyl group.

Among these compounds, a trialkylaluminum is preferable andtriisobutylaluminum is particularly preferable.

These organic aluminum compounds (B-2) may be used alone or incombination of two or more.

((B-3) Compounds Which React with the Metallocene Compound (A) to Forman Ion Pair)

Examples of the compound (B-3) which reacts with the metallocenecompound (A) to form an ion pair may include Lewis acids, ioniccompounds and carborane compounds described in each publication ofJapanese Patent Application Laid-Open Nos. 1-501950, 1-502036, 3-179005,3-179006, 3-207703 and 3-207704 and in the specification of U.S. Pat.No. 547718.

Examples of the Lewis acid include triphenylboron,tris(4-fluorophenyl)boron, tris(p-tolyl)boron, tris(o-tolyl)boron,tris(3,5-dimethylphenyl)boron, tris(pentafluorophenyl)boron, MgCl₂,Al₂O₃ and SiO₂—Al₂O₃.

Examples of the ionic compound include triphenylcarbeniumtetrakis(pentafluorophenyl) borate, tri-n-butylammoniumtetrakis(pentafluorophenyl) borate,N,N-dimethylaniliniumtetrakis(pentafluorophenyl) borate andferroceniumtetra(pentafluorophenyl) borate.

Examples of the carborane compound include dodecaborane,1-carbaundecaborane, bis-n-butylammonium (1-carbedodeca) borate,tri-n-butylammonium (7,8-dicarbaundeca) borate and tri-n-butylammonium(tridecahydride-7-carbaundeca) borate.

These compounds may be used alone or in combination of two or more.

In the present invention, at least one compound selected from thecomponents (B-1), (B-2) and (B-3) as aforementioned is used as theco-catalyst component (B) and these components may be also used incombination adequately. It is desirable to use at least the component(B-1) or (B-2) among these components as the co-catalyst component (B).

In the present invention, it is desirable to use a catalyst containingthe aforementioned metallocene catalyst component and co-catalystcomponent and typically, it is preferred to use this catalyst as asupported-on-a-support type catalyst (solid catalyst) made by contactingthese catalyst components with a support compound in particle form.

As the support compound, a granular or particulate solid having aparticle diameter of 10 to 300 μm and preferably 20 to 200 μm is used.This support preferably has a specific surface area of typically 50 to1000 m²/g and a pore volume of 0.3 to 2.5 cm³/g.

As such a support, porous inorganic oxides are preferably used.Specifically, SiO₂, Al₂O₃, MgO, ZrO₂, TiO₂, B₂O₃, CaO, ZnO, BaO, ThO₂and the like or mixtures of these compounds, for example, SiO₂—MgO,SiO₂—Al₂O₃, SiO₂—TiO₂, SiO₂—V₂O₅, SiO₂—Cr₂O₃, SiO₂—TiO₂—MgO and the likeare used. Among these compounds, those having SiO₂ and/orAl₂O₃as theirmajor components are preferable.

The above inorganic oxide may contain carbonates, sulfates, nitrates andoxide components such as Na₂CO₃, K₂CO₃, CaCO₃, MgCO₃, Na₂SO₄, Al₂(SO₄)₃, BaSO₄, KNO₃, Mg(NO₃)₂, Al(NO₃)₃, Na₂O, K₂O and Li₂O in a smallamount.

As the support, organic compounds may be also used. For example,(co)polymers produced using olefins having 2 to 14 carbon atoms such asethylene, propylene, 1-butene and 4-methyl-1-pentene as the majorcomponents or polymers or copolymers produced using vinylcyclohexene andstyrene as the major component may be used.

It is desirable that the contact of the support and the above eachcomponent is carried out at a temperature of typically −50 to 150° C.and preferably −20 to 120° C. for 1 minute to 50 hours and preferably 10minutes to 25 hours.

In the solid catalyst prepared in the above manner, the metallocenecompound (A) is preferably supported in an amount of 5×10⁻⁶ to 5×10⁻⁴gram atom and preferably 10⁻⁵ to 2×10⁻⁴ gram atom as a transition metalper 1 g of the support and the component (B) is preferably supported inan amount of 10⁻³ to 5×10⁻² gram atom and preferably 2×10⁻³ to 2×10⁻²gram atom as an aluminum atom or a boron atom per 1 g of the support.

Further, in the present invention, although the solid catalyst asaforementioned may be used for polymerization as it is, it may be usedin the form of a pre-polymerized catalyst formed by pre-polymerizing theolefin thereon.

In the present invention, the solid catalyst or the pre-polymerizedcatalyst is preferably used in an amount of typically 10⁻⁸ to 10⁻³ gramatom/litter and further 10⁻⁷ to 10⁻⁴ gram atom/1 in terms of transitionmetal/litter (polymerization volume).

In addition, although the component (B) may be used or not when usingthe pre-polymerized catalyst, it may be used, according to the need, inan amount of 5 to 300, preferably 10 to 200 and more preferably 15 to150 in terms of the atomic ratio of aluminum or boron (Al/transitionmetal or B/transition metal) to the transition metal in thepolymerization system.

The density (ASTM D150E) of the olefinic polymer obtained in the abovemanner is preferably 0.865 to 0.930 g/cm³ and more preferably 0.880 to0.930 g/cm³.

When the olefinic polymer is an ethylene/α-olefin copolymer, thecopolymer preferably contains the structural unit derived from ethylenein an amount of 87.0 to 97.6 mol % and preferably 90.0 to 96.8 mol % andthe structural unit derived from α-olefins having 3 to 10 carbon atomsin an amount of 13.0 to 2.4 mol % and preferably 10.0 to 3.2 mol %.

It should be noted that the olefinic polymer may contain the unitderived from polyenes and the like in an amount of 10% by weight orless, preferably 5% by weight or less and particularly preferably 3% byweight or less.

(Ligand Removing Step)

The polymer particle ((co)polymer) withdrawn from the discharge lines(10, 40) in the polymerization step as mentioned above is fed to theligand removing step where the ligand in the polymer particle isremoved.

The ligand removing step comprises (1) a step (catalyst decomposingstep) of decomposing a catalyst by bringing the (co)polymer obtained inthe above polymerization step into contact with a ligand-remover todecompose catalyst to metal and ligand in the (co)polymer and (2) a step(ligand eliminating step) of heating the above (co)polymer which hasbeen made to be in contact with the ligand-remover and eliminating theligand liberated during the above-mentioned catalyst decomposing stepfrom the (co)polymer.

(Ligand-Remover)

Given as examples of the ligand-remover used in the catalyst decomposingstep are water, oxygen, alcohols, alkylene oxides and peroxides.Specific examples of the ligand-remover include alcohols having 10 orless carbon atoms such as mono-alcohols, e.g., methanol, ethanol,propanol, isopropanol, butanol, pentanol, hexanol, heptanol, octanol,cyclopentanol and cyclohexanol and dialcohols, e.g., ethyleneglycol;alkylene oxides such as ethylene oxide, propylene oxide, trimethyleneoxide, tetrahydrofuran and tetrahydropyran; and peroxides such aspropylene peroxide and butene peroxide.

Among these compounds, water and alcohols having 5 or less carbon atomsare preferable and water is particularly preferable.

As a method of bringing the (co)polymer into contact with theligand-remover, there is a method in which the (co)polymer is broughtinto contact with a gas stream containing the ligand-remover. In thiscase, a powder of the (co)polymer is allowed to pass through a vesselwhile introducing gas containing the ligand-remover into the vessel.

The average particle diameter of the powder of the (co)polymer when the(co)polymer is brought into contact with the ligand-remover is in arange from typically 50 to 5,000 μm, preferably 80 to 3,000 μm and morepreferably 100 to 2,000 μm. Examples of the gas for dilution of theligand-remover include inert gases such as nitrogen gas and argon gas.In the ligand-remover-containing gas, a vapor of the ligand-remover istypically contained. The proportion of the ligand-remover in theligand-remover-containing gas is in a range from typically 0.1% byweight to 40% by weight, preferably 0.5% by weight to 20% by weight andparticularly preferably 1% by weight to 10% by weight.

The space tower velocity of the ligand-remover-containing gas is in arange from typically 0.01 to 20 cm/sec, preferably 0.1 to 10 cm/sec andparticularly preferably 0.5 to 5 cm/sec. The space tower velocity iscalculated based on the temperature and pressure of theligand-remover-containing gas at the gas exit port of an apparatus usedwhen bringing the (co)polymer into contact with the ligand-remover andthe sectional area of the apparatus.

The temperature used when bringing the (co)polymer into contact with theligand-remover is typically more than the crystallization temperature ofthe (co)polymer and less than the decomposition temperature of the(co)polymer and, specifically, in a range from 100 to 300° C. andpreferably 100 to 280° C. when the crystallinity of the (co)polymer is40% or more. When the crystallinity of the (co)polymer is less than 40%,the temperature is equal to or more than the temperature of the meltingpoint of the (co)polymer minus 15° C., and less than the decompositiontemperature of the (co)polymer and specifically in a range from 85 to300° C. and preferably 90 to 280° C.

It should be noted that the degree (X_(c)) of crystallization of the(co)polymer is measured by the following method. Specifically, the(co)polymer is pre-heated at 190° C. for 7 minutes and then pressed at9.8 MPa for 2 minutes. Thereafter, the (co)polymer is cooled under thecondition of 20° C. and 9.8 MPa to produce a 5-mm-thick pressed sheet.About 5 mg of a test piece (sample) cut from the above pressed sheet isplaced in an aluminum pan. Using DSC-II (manufactured by Perkin ElmerInc.), measurement is made from room temperature to 150° C. withincreasing the temperature by 10° C./min to obtain an endothermic curve.The endothermic curve of the sample is converted into a curve of calorieof melting using the endothermic curve area of indium which has beenseparately measured. The point at 35° C. on the endothermic curve of thesample is connected to the point at which the heat absorption peakdisappeared completely to make a base line. The value (X_(c)=A/260)obtained by dividing the calorie of melting (A (J/g)) from themeasurement by the calorie of melting (260(J/g)) of a 100% polyethylenecrystal is expressed as the crystallinity.

The pressure when bringing the (co)polymer into contact with theligand-remover is in a range of typically 0.0001 to 0.6MPa, preferably0.001 to 0.35 MPa and particularly preferably 0.01 to 0.25 MPa. Thecontact time (retention time) is typically 1 minute to 3 hours,preferably 2 minutes to 2 hours and particularly preferably 5 minutes to1 hour.

The catalyst can be decomposed, so that the ligand having a high-boilingpoint can be converted into low-boiling point compounds by bringing the(co)polymer into contact with the ligand-remover as aforementioned.Also, the ligand is occasionally made odorless by only the decompositiondepending on the type of ligand.

Next, the (co)polymer which has been brought into contact with theligand-remover is heated to remove the decomposed ligand in the(co)polymer. As a method of eliminating the ligand by heating the(co)polymer which has been made to be in contact with theligand-remover, there is, for example, the following methods.

(1) A method in which the (co)polymer is heated using a dryer such as arotary drier, belt drier, flash drier, spray drier or puddle drier undera stream of inert gas.

(2) A method in which the (co)polymer is heated and melted using asingle-screw or twin-screw extruder.

In the case of adopting the method (2), the heat-melted (co)polymer ispelletized and may be further subjected to any of the following steps(2-1) to (2-3).

(2-1) A step of bringing the pellet into contact with hot water.

(2-2) A step of bringing the pellet into contact with steam.

(2-3) A step of heating the pellet under a pressure of 0.001 to 0.098MPa.

The heating temperature of the (co)polymer when carrying out the abovemethod (1) is typically more than the crystallization temperature of the(co)polymer and less than the decomposition temperature of the(co)polymer or more than the crystallization temperature of the(co)polymer and lower than the melting point of the (co)polymer, and,specifically, in a range from 100 to 300° C. and preferably 100 to 280°C. when the crystallinity of the (co)polymer is 40% or more.

When the crystallinity of the (co)polymer is less than 40%, thetemperature is the melting point of the (co)polymer −15° C. or more andless than the decomposition temperature of the (co)polymer or is themelting point of the (co)polymer −15° C. or more and less than themelting point of the (co)polymer, and is specifically in a range from 85to 300° C. and preferably 90 to 280° C.

The pressure is in a range of typically 0.0001 to 0.6 MPa, preferably0.001 to 0.35 MPa and particularly preferably 0.01 to 0.25 MPa. Theheating time (retention time) is typically 1 minute to 3 hours,preferably 2 minutes to 2 hours and particularly preferably 5 minutes to1 hour.

Examples of the inert gas include nitrogen gas, helium gas and argongas. The gas flow rate in the drier is in a range from typically 0.01 to20 cm/sec, preferably 0.1 to 10 cm/sec and particularly preferably 0.5to 5 cm/sec.

When carrying out the above method (2), the heating temperature of the(co)polymer is the same as in the method (1). In the present invention,in the case of heating the (co)polymer at a temperature more than themelting point of the (co)polymer and less than the decompositiontemperature of the (co)polymer in the ligand eliminating step, it ispreferable to heat with applying shear stress to the (co)polymer.Examples of a method for applying shear stress to the (co)polymerinclude methods using a paddle drier or a single-screw or twin-screwextruder.

In the case of adopting the above method (2) in the present invention,the heat-melted (co)polymer is pelletized and maybe subjected to any ofthe following steps (2-1) to (2-3).

As an apparatus which may be used when carrying out a step (2-1), thereare a counter-current extracting tower, tank provided with a stirrer andmultistage horizontal extracting vessel. As an apparatus which may beused when carrying out steps (2-2) and (2-3), there are a silo andhopper.

When carrying the above step (2-1), the temperature of the hot water isin a range from 35 to 200° C., preferably 40 to 180° C. and particularlypreferably 45 to 150° C. The contact time is in a range from 1 to 900minutes, preferably 5 to 600 minutes and particularly preferably 10 to360 minutes.

In the step (2-2), similarly to the aforementioned ligand removing step,steam-containing gas is brought into contact with the (co)polymer.Examples of the steam-containing gas include inert gas and air which arethe same as above.

The heating temperature of the (co)polymer when bringing the (co)polymerinto contact with the steam-containing gas is typically more than thecrystallization temperature of the (co)polymer and less than thedecomposition temperature of the (co)polymer or more than thecrystallization temperature of the (co)polymer and lower than themelting point of the (co)polymer, and, specifically, in a range from 100to 300° C. and preferably 100 to 280° C. when the crystallinity of the(co)polymer is 40% or more.

When the crystallinity of the (co)polymer is less than 40%, thetemperature is the melting point of the (co)polymer −15° C. or more andless than the decomposition temperature of the (co)polymer or is themelting point of the (co)polymer −15° C. or more and less than themelting point of the (co)polymer, and is specifically in a range from 85to 300° C. and preferably 90 to 280° C.

The pressure is in a range of typically 0.0001 to 0.6 MPa, preferably0.001 to 0.35 MPa and particularly preferably 0.01 to 0.25 MPa. Theproportion of the steam in the steam-containing gas is in a range fromtypically 0.1% by weight to 40% by weight, preferably 0.5% by weight to20% by weight and particularly preferably 1% by weight to 10% by weight.

The space tower velocity of the steam-containing gas is in a range fromtypically 0.01 to 20 cm/sec, preferably 0.1 to 10 cm/sec andparticularly preferably 0.5 to 5 cm/sec. The contact time (retentiontime) is typically 0.5 to 30 hours, preferably 1 to 24 hours andparticularly preferably 2 to 20 hours.

When carrying out the above step (2-3), the pressure is in a range from0.001 to 0.100 MPa, preferably 0.007 to 0.098 MPa and particularlypreferably 0.01 to 0.07 MPa. The temperature is 35to 200° C., preferably40 to 180° C. and particularly preferably 45 to 150° C. Also, theheating time is 0.5 to 30 hours, preferably 1 to 24 hours andparticularly preferably 2 to 20 hours.

It is desirable that the average particle diameter of the (co)polymerpellet when carrying out the above steps (2-1) to (2-3) be in a rangefrom typically 1 to 30 mm, preferably 3 to 20 mm and more preferably 5to 15 mm.

To state more specifically, the step of removing the ligand of the(co)polymer may be carried out using, for example, a step as shown inFIG. 3 or FIG. 4. FIG. 3 shows an explanatory view representing oneexample of the ligand removing step and FIG. 4 shows an explanatory viewrepresenting another example of the ligand removing step. In a silorepresented by 51 in the figure, the catalyst decomposing step iscarried out and in an extruder represented by 52, a silo represented by54 and a drier represented by 57 in the figure, the ligand eliminatingstep is carried out.

An example in which water (steam) is used as the ligand-remover will behere in after explained. In the step shown in FIG. 3, the powder of the(co)polymer is supplied continuously from a powder supply pipe 61 to thesilo 51. In the silo 51, inert gas containing steam is supplied to thesilo 51 from a gas supply pipe 62 disposed on the lower part thereof. Bythis measure, the powder of the (co)polymer is brought into contact withthe steam and the catalyst contained in the (co)polymer is decomposed.The steam-containing inert gas supplied to the silo is discharged from agas discharging pipe 64 to the outside of the silo 51.

The powder of the (co)polymer which is in contact with the steam isdischarged to the outside of the silo 51 from a powder discharge pipe 63and then supplied to an extruder 52. The (co)polymer which isheat-melted in the extruder 52 is cooled by water and pelletized. Bythis measure, a part of the ligand liberated during catalyst decomposingstep contained in the (co)polymer is removed. The obtained (co)polymerpellet is supplied together with water to a dehydrator 53 through a line65. The dehydrated (co)polymer pellet is supplied to the silo 54 througha pellet supply pipe 67. The water separated by the dehydrator 53 isreused as cooling water through a circulating line 66. In the figure, 55represents a water storage tank and 56 represents a pump.

In the silo 54, steam-containing inert gas is supplied to the silo 54from a gas supply pipe 68 disposed on the lower part thereof. By thismeasure, the (co)polymer pellet is brought into contact with the steam,so that ligand generated from the decomposed catalyst contained in the(co)polymer is further removed. The steam-containing inert gas suppliedto the silo 54 is discharged to the outside of the silo 54 from a gasdischarge pipe 70. The (co)polymer pellet from which the decomposedcatalyst ligand has been removed is discharged from a pellet dischargepipe 69.

In the step shown in FIG. 4, the (co)polymer powder is in contact withthe steam-containing inert gas in the silo 51 where the catalystcontained in the (co)polymer is decomposed to metal and ligand. The(co)polymer powder which has been in contact with the steam isdischarged to the outside of the silo 51 from the powder discharge pipe63 and then supplied to the drier 57. It should be noted that the drier57 is a belt drier, but is not limited to this type.

In the drier 57, heated inert gas is supplied from a gas supply pipe 71and the (co)polymer powder is heated and also brought into contact withthe inert gas. The ligand liberated by the catalyst decompositioncontained in the (co)polymer is thereby removed. The inert gas suppliedto the drier 57 is discharged from a gas discharge pipe 72.

The (co)polymer powder from which the decomposed catalyst has beenremoved is supplied to a crasher 58 through a line 73. In the crasher,the (co)polymer is crashed and then discharged from a discharge pipe 74.

In the ligand removing step, the ligand having a cyclopentadienylstructure left in the (co)polymer is decomposed and removed from the(co)polymer obtained in the polymerization step. Therefore, a polyolefinreduced in the emanation of odors during molding can be obtained.

Effect of the Invention

The olefinic polymer of the present invention is reduced in the contentof low-molecular weight components such as oligomers and a ligand havinga cyclopentadienyl structure which are components generating odors andchanging tastes. The olefinic polymer is therefore reduced in thecontent of components generating odors and changing tastes when used infood uses and therefore scarcely damages the fragrance of foods.

The process of the present invention for producing an olefinic polymercan produce an olefinic polymer reduced in the content of low-molecularweight components such as oligomers and a ligand having acyclopentadienyl structure which are components generating odors andchanging tastes at low costs in a well producible manner.

EXAMPLES

The present invention will be hereinafter explained in more detail byway of examples, which, however, are not intended to be limiting of thepresent invention.

Example 1

(Preparation of a Solid Catalyst Component)

10 kg of silica (SiO₂) which had been dried at 250° C. for 10 hrs wassuspended in 154 l of toluene, which was then cooled to 0° C. To thesuspension was added dropwise 50.5 1 of a toluene solution ofmethylaluminoxane (Al=1.52 mol/l) over one hour with keeping thetemperature of the suspension at 0 to 5° C. In succession, the resultingsolution was kept at 0° C. for 30 minutes, then raised to 95° C. over1.5 hours and kept at 95° C. for 4 hours.

Thereafter, the temperature was dropped to 60° C. and the supernatantwas removed by decantation. The solid catalyst component obtained inthis manner was washed twice with toluene and then re-dispersed in 100 lof toluene to be a total amount of 160 l. 22.0 1 of a toluene solutionof bis(1,3-n-butylmethylcyclopentadienyl)zirconium dichloride (Zr=25.7mmol/l) was added to the obtained suspension at 80° C. over 30 minutesand the resulting solution was further kept at 80° C. for 2 hours.Thereafter, the supernatant was removed and the residue was washed twicewith hexane to obtain a solid catalyst component containing zirconium inan amount of 3.2 mg per 1 g of silica.

(Pre-Polymerization of the Solid Catalyst Component)

A 350 l reactor in which the atmosphere was thoroughly replaced bynitrogen was charged with 7.0 kg of the above solid catalyst componentand then filled with hexane to prepare a hexane suspension having atotal amount of 285 1. The system was cooled to 0° C. and then ethylenewas blown into the hexane suspension of the solid catalyst component ata rate of 8 Nm³/hr for 5 minutes. During this time, the systemtemperature was kept at 10 to 15° C.

After the supply of ethylene was suspended for a time, 2.4 mol oftriisobutylaluminum and 1.2 kg of 1-hexene were supplied to the system,which was then made to be a closed system and then, the supply ofethylene was resumed. Ethylene was supplied at a flow rate of 8 Nm3/hrfor 15 minutes and then flow rate was dropped to 2 Nm³/hr to set thepressure in the system to 0.8 kg/cm² ·G. During this operation, thetemperature of the system was raised to 35° C.

Thereafter, ethylene was supplied at a flow rate of 4 Nm³/hr for 3.5hours with controlling the system temperature to 32 to 35° C. Duringthis operation, the pressure in the system was kept under 0.7 to 0.8kg/cm² ·G. Next, the atmosphere in the system was replaced by nitrogenand the supernatant was removed. Then, the residue was washed twice withhexane. The supernatant obtained after the washing of the prepolymerizedcatalyst was colorless and transparent.

A prepolymerized catalyst containing 3 g of a prepolymer per 1 g of thesolid catalyst component was obtained in the above manner. The intrinsicviscosity [η] of this prepolymerized catalyst component (prepolymer)which was measured at 135° C. in decaline was 2.1 dl/g and the contentof 1-hexene units was 4.8% by weight. The prepolymerized catalyst had agood shape and a bulk density of 0.4 g/cm³.

(Vapor Phase Polymerization)

A continuous fluidized-bed reactor as shown in FIG. 1 was used to carryout vapor phase polymerization.

Specifically, the prepolymerized catalyst obtained in the above mannerwas continuously supplied at a rate of 54 g/hr to polymerize ethylenewith 1-hexene continuously in the presence of isopentane to obtain alinear low-density polyethylene (LLDPE).

The process was carried out in the following condition: polymerizationtemperature: 70° C., polymerization pressure: 1.7 MPa-G (gage pressure),partial pressure of ethylene: 1.1 MPa, space tower velocity: 0.80 m/sand concentration of isopentane in the gas (TOP gas) in the decelerationregion of the reactor: 5 mol %. During this polymerization, the averagemolecular weight of the TOP gas was 31.4 g/mol and the density of theTOP gas was 20.7 kg/m³. Also, the dew point of the TOP gas was 40.1° C.,the temperature of the outlet side of the circulating gas in the heatexchanger was 62.3° C. and the ratio of the condensed liquid at theoutlet side of the circulating gas was 0% by weight.

The above TOP gas is a mixture of ethylene, nitrogen, hydrogen, 1-hexeneand isopentane.

The LLDPE obtained in the above manner had a density (ASTM D1505) of 903kg/m³ and an MFR (ASTM D1238) was 3.8 g/10 minutes.

(Catalyst Decomposing Step)

A powder of the above LLDPE was allowed to pass through a silo, intowhich steam-containing nitrogen gas was introduced and the pressure andthe temperature were set to 0.5 kPa-G and 80° C. respectively, for aretention time of 5 minutes.

At this time, the ratio (water/PE) by weight of the water to thepolyethylene powder (PE) was 0.001 and the ratio (N₂ (N-m³)/PE (kg)) ofthe nitrogen gas to the polyethylene powder (PE) was 0.004.

(Ligand Eliminating Step)

The LLDPE powder treated in the above catalyst decomposing step waspelletized at an outlet temperature of 205° C. using a twin-screwextruder. Thereafter, the above LLDPE powder treated in the abovecatalyst decomposing step was allowed to pass through a silo, into whichsteam-containing air gas was introduced and the pressure and thetemperature were set to 0.5 kPa-G and 80° C. respectively, for aretention time of 6 hours.

At this time, the ratio (water/PE) by weight of the steam (water) to thepolyethylene pellet (PE) was 0.09 and the ratio (air (N-m³)/PE (kg)) ofthe air to the polyethylene pellet (PE) was 0.14.

(Evaluation)

The LLDPE treated in the above manner was evaluated as to the residualamount of the ligand, n-decane-soluble content and odors. The resultsare shown in Table 1.

The odor of the LLDPE treated in the above manner was evaluated in thefollowing manner.

⊚: None of the three panelists felt any odor.

◯: One panelist among the three panelists felt some odors, but didn'tfeel a strong odor.

Δ: Two or three panelists among the three panelists felt some odors, butdidn't feel a strong odor.

x: All of the three panelists felt a strong odor.

Examples 2 to 4 and Comparative Examples 1 to 6

LLDPEs were obtained in the same manner as in Example 1 except that theconcentration of isopentane contained in the TOP gas in the polymerizingvessel, the average molecular weight of the TOP gas in the polymerizingvessel, the density of the gas in the polymerizing vessel, the gastemperature at the outlet side of the circulating gas in the heatexchanger and the like were changed to the conditions shown in Table 1in Example 1.

The residual amount, n-decane-soluble content and odors of the resultingLLDPE were evaluated in the same manner as in Example 1. The results areshown in Table 1. Incidentally, in the Table 1, first line, abbreviation‘EX’ and ‘CE’ means example and Comparative Example respectively.

TABLE 1 UNIT CE-1 CE-2 CE-3 CE-4 CE-5 EX-1 EX-2 CE-6 EX-3 EX-4Polymerization temperature ° C. 70 70 70 70 70 70 70 70 70 70Polymerization pressure MPaG 1.7 1.7 1.7 1.7 1.7 1.7 1.7 1.7 1.7 1.7 Gasspace tower velocity m/s 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8Composition of the TOP gas in the polymerization vessel Ethylene mol %55.5 55.5 55.5 55.5 55.5 55.5 55.5 55.5 55.5 55.5 Hexene-1 mol % 1.9 1.91.9 1.9 2 2 2 1.9 1.9 1.9 Hydrogen mol ppm 333 333 333 333 340 340 340326 326 326 Nitrogen mol % 42.3 42.3 42.3 42.3 36.7 36.7 36.7 28.5 28.528.5 Isopentane mol % 0 0 0 0 5 5 5 15 15 15 Average molecular weight ofthe g/mol 29.2 29.2 29.2 29.2 31.4 31.4 31.4 35.8 35.8 35.8 TOP gas inthe polymerization vessel Density of the gas in the kg/m3 19 19 19 1920.7 20.7 20.7 24.3 24.3 24.3 polymerization vessel Dew point of the gasin the ° C. 24.1 24.1 24.1 24.1 40.1 40.1 40.1 62 62 62 polymerizationvessel Gas temperature at the outlet ° C. 61.5 61.5 61.5 61.5 62.3 62.362.3 63.5 63.5 63.5 side of the circulating gas in the heat exchangerRatio of the condensed liquid wt % 0 0 0 0 0 0 0 0 0 0 at the outletside of the circulating gas in the heat exchanger Supply amount of theg/h 58 58 58 58 54 54 54 49 49 49 prepolymerized catalyst Polymerizedamount kg/h 100 100 100 100 100 100 100 100 100 100 Polyethylene Densitykg/m3 903 904 903 903 902 903 904 901 903 902 MFR g/10 min 3.7 3.9 3.63.8 3.8 3.8 3.5 3.9 3.5 3.4 Retention time hrs 3 3 3 3 3 3 3 3 3 3 STYkg/h · 100 100 100 100 100 100 100 100 100 100 m3 Catalyst activity *16900 6900 6900 6900 7400 7400 7400 8200 8200 8200 Powder steaming timemin 0 5 5 5 0 5 5 0 5 5 Pellet steaming time hrs 0 6 12 30 0 6 12 0 6 12Concentration of the ligand ppb 10 1 <1 2 10 1 <1 9 1 <1n-Decane-soluble content wt % 12.2 11.8 11.1 11.6 8.4 8.1 7.5 2.3 2.21.9 Odor — X X Δ ◯ X ◯ ⊚ X ⊚ ⊚ *1 g-PE/g-Bare Cat.

1. An olefinic (co)polymer obtained by polymerizing at least oneselected from the group consisting of ethylene and α-olefins having 3 to20 carbon atoms in the presence of a metallocene type catalyst in thegas phase with allowing a saturated aliphatic hydrocarbon having 2 to 10carbon atoms to exist in a concentration of 2 to 30 mol % in afluidized-bed reactor, next bringing the resulting (co)polymer intocontact with a ligand-remover and then heating said (co)polymer whichhad been brought into contact with the ligand-remover, wherein then-decane-soluble content of the polymer is 1.9–10% by weight and thecontent of a ligand having a cyclopentadienyl structure is 5 ppb byweight or less.
 2. An olefinic polymer according to claim 1, wherein theolefinic polymer is a copolymer of ethylene and at least one α-olefinselected from α-olefins having 3 to 20 carbon atoms.
 3. An olefinicpolymer according to claim 1 or 2, wherein the polymer has a density of0.930 g/cm³ or less.